This invention relates generally to a means for connecting together the ends of at least one pair of optical fibers and more particularly to a means for making such a connection wherein the cores of the fibers are better aligned than has been heretofore possible.
One of the problems in the development of optical waveguides for the transmission of modulated light has been the making of in-line connections between the ends of one or more pairs of optical fibers. Such problem consists essentially of the lateral alignment of the two cores of each pair of optical fibers and arises primarily from two causes. One such cause is the variation in the thickness of the optical cladding (hereinafter also referred to simply as cladding) around the core of the optical fiber, which thickness can vary over one hundred percent. For example, in one commercially available optical fiber the nominal thickness of the plastic cladding is about three thousandths of an inch, with the core diameter being about six thousandths of an inch. However, the thickness of the cladding can vary from about one to six thousandths of an inch. Obviously, referencing the alignment of two fibers together by means of the outside diameters of the cladding can result in serious misalignment of the cores. The second major difficulty presented is that the diameter of the cores themselves can vary substantially. A connector for aligning two fibers with reference to the cladding thereon in a concentric manner is disclosed in copending application Ser. No. 768,512 filed Feb. 14, 1977, by William Ludlow Schumacher and entitled "Overlap Type Waveguide Connector Assembly And Method". This Ser. No. 768,512 application grips the cables or fiber at three different points. More specifically, each cable, including its outer sheath, is gripped by a first portion of a first half of the complete connector to provide a coarse alignment of the cables and the fibers therein. Such first portion also provides a datum plane from which to measure an extended portion of optical fiber so that the end thereof will properly mate with the end of another optical fiber contained within a first portion of the second half of the complete connector. Each connector half portion further comprises a second portion which has first grooves formed therein to retain and to provide secondary lateral alignment of the fibers. Preferably both first and second connector halves and their second parts are constructed of rigid material. Each connector half further comprises a third portion made of an elastomeric material which has second, semi-cylindrically shaped grooves formed therein, with each second groove receiving one of the fibers from the second portion of the connector. The grooves contained within the two elastomeric portions are designed to mate with each other to form a cylindrical channel within which a pair of fibers to be connected in an in-line manner terminate with their ends being in very close proximity to each other but without actually touching. Because of the properties of the elastomeric material the two fibers of each pair are aligned with each other in a substantially concentric manner measured from the outside circumference of the cladding. However, because of the wide variation thickness of the cladding, the cores of the fibers are frequently badly misaligned with substantial loss of signal integrity.
Further, with many currently available optical fibers, the cladding is very fragile and often will rupture when pressed between two elastomeric pads, thereby exposing the core to a surface whose index of refraction is higher than that of the core. Perturbation of the light signal results. An additional problem presented with certain types of cladding is that it is difficult to score and break the end of the core in a smooth plane normal to the axis of the core. The cladding interferes with the scoring to produce a non-planar break of the core.